Agricultural combines are large machines that harvest, thresh, separate and clean an agricultural crop. The resulting clean grain is stored in a grain tank located on the combine. The clean grain can then be transported from the grain tank to a truck, grain cart or other receiving bin by an unloading auger.
Rotary combines have a rotary crop processing unit formed by a rotor and a casing surrounding the rotor. The rotary crop processing unit has an inlet transition section for pulling crop material into a rotary crop processing unit from the feederhouse. The rotary crop processing unit includes a threshing section for threshing the crop material and a separating section for separating the grain from the threshed crop material. The bottom of the casing is provided with a series of grates through which the grain and chaff fall from the casing. The grates, located beneath the threshing section of the rotary crop processing unit, comprise a concave.
Crop material, especially green crop material and high volume crop material, tends to plug the concave, not allowing grain to pass through the concave and thus reducing capacity and threshing ability. Furthermore, in some rotary combines, it is necessary to change between two different concaves, with different sized openings, when changing between harvesting of small and large grain crops.